Many small internal combustion engines are supplied with a combustible charge of air and fuel using a carburetor. A typical carburetor includes a body at least partially defining a liquid fuel chamber, an air and fuel mixing passage, and one or more fuel passages in communication between the fuel chamber and the air and fuel mixing passage. The fuel passages communicate with the mixing passage between an air inlet at an upstream end and an air-and-fuel mixture outlet at a downstream end. Typically, a choke valve is disposed in the air and fuel mixing passage near the upstream end to control a quantity of air flowing into the mixing passage during engine cold starting and warm up. A throttle valve is disposed in the air-and-fuel mixing passage near the downstream end to control a quantity or flow rate of the air-and-fuel mixture flowing out of the mixing passage to the operating engine.